Well, since OS2008 is the first release to support transparency on the tasknavigator, statusbar, and desktop applets, you probably won't find a theme like that for 770 (unless Nokia releases an OS2008 hacker edition).

As for theming resources, there is a howto, but it's for OS2008.
http://live.gnome.org/Hildon/ThemeHowTo

To make themes for earlier OS releases, you might try Urho Konttori's ThemeMaker: https://garage.maemo.org/projects/thememaker/

Older versions (which are still available) produced themes which worked on OS2006 and 2007, but I'm not sure about the latest release.

Good luck.